Image sensor and electronic device including the same

ABSTRACT

This technology provides an image sensor and an electronic device including the same. In an image sensor including a pixel array including a plurality of unit pixels, each of the plurality of unit pixels may include a photoelectric conversion element and a pixel lens over the photoelectric conversion element and comprising a plurality of light condensing layers in which a lower layer has a larger area than an upper layer, wherein the pixel lens has a shape changing based on a position of a corresponding unit pixel from a center of the pixel array to an edge of the pixel array.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Korean Patent ApplicationNos. 10-2014-0117884 and 10-2015-0080999, filed on Sep. 4, 2014 and Jun.9, 2015, respectively, which are herein incorporated by reference intheir entirety.

BACKGROUND

Exemplary embodiments of the present invention relate to a semiconductordevice manufacturing technology, and more particularly, to an imagesensor including a light condensing member having a multilayer steppedshape and an electronic device including the same.

An image sensor converts an optical age into electrical signals. Due tothe development of the computer and communication industries, the demandfor image sensors with improved performance has increased in variousfields such as digital cameras, camcorders, Personal CommunicationSystems (PCS), game machines, security cameras, medical micro-cameras,and robots.

SUMMARY

Various embodiments are directed to an image sensor having improvedperformance and an electronic device including the same.

In an embodiment, in an image sensor including a pixel array including aplurality of unit pixels, wherein each of the plurality of unit pixelsmay include a photoelectric conversion element; and a pixel lens overthe photoelectric conversion element and comprising a plurality of lightcondensing layers in which a lower layer has a larger area than an upperlayer, wherein the pixel lens has a shape changing based on its positionfrom a center of the pixel array to an edge of the pixel array.Furthermore, each of the plurality of unit pixels may further include afocusing layer between the photoelectric conversion element and thepixel lens; a color filter layer covering the pixel lens; and ananti-reflection structure over the color filter layer.

The pixel lens may be symmetrical based on a central axis of each of theplurality of unit pixels and an area of the pixel lens may be graduallyincreased from the center of the pixel array to the edge of the pixelarray. A width of the lower layer exposed by the upper layer in theplurality of light condensing layers may be constant regardless of itsposition in the pixel array. The width of the lower layer exposed by theupper layer may be smaller than a wavelength of incident light.

The pixel lenses of each of the plurality of unit pixels may be the samesize, and asymmetry of the pixel lens may be gradually increased basedon a central axis of each of the plurality of unit pixels going from thecenter of the pixel array to the edge of the pixel array. A maximumwidth of the lower layer exposed by the upper layer in the plurality oflight condensing layers may be gradually increased going from the centerof the pixel array to the edge of the pixel array. The maximum width ofthe lower layer exposed by the upper layer may be smaller than awavelength of incident light. The upper layer of the plurality of lightcondensing layers may be shifted more to the center of the pixel arraybased on the central axis of each of the plurality of unit pixels goingfrom the center of the pixel array to the edge of the pixel array. Onthe other hand, the upper layer of the plurality of light condensinglayers may be shifted more to the edge of the pixel array based on thecentral axis of each of the plurality of unit pixels going from thecenter of the pixel array to the edge of the pixel array.

The pixel lens may have a multilayer stepped shape. The plurality oflight condensing layers of the pixel lens may have the same shape andmay be parallel to each other. A thickness of the upper layer of theplurality of light condensing layers may be less than or equal to athickness of the lower layer. A refractive index of the upper layer ofthe plurality of light condensing layers may be less than or equal to arefractive index of the lower layer.

In an embodiment, an electronic device may include an optical system; animage sensor suitable for receiving light from the optical system andcomprising a pixel array including a plurality of unit pixels; and asignal processing unit suitable for performing a signal processingoperation on a signal output from the image senso. Each of the pluralityof unit pixels of the image sensor may include a photoelectricconversion element; and a pixel lens over the photoelectric conversionelement and comprising a plurality of light condensing layers in which alower layer has a larger area than an upper layer, wherein the pixellens has a shape changing based on a position of a corresponding unitpixel going from a center of the pixel array to an edge of the pixelarray. Furthermore, each of the plurality of unit pixels may furtherinclude a focusing layer between the photoelectric conversion elementand the pixel lens; a color filter layer covering the pixel lens; and ananti-reflection structure over the color filter layer.

The pixel lens may be symmetrical based on a central axis of each of theplurality of unit pixels and an area of the pixel lens may be graduallyincreased going from the center of the pixel array to the edge of thepixel array. The pixel lenses of the unit pixels may be the same size,and asymmetry of the pixel lens may be gradually increased based on acentral axis of each of the plurality of unit pixels from the center ofthe pixel array to the edge of the pixel array. The pixel lens may havea multilayer stepped shape. A width of the lower layer exposed by theupper layer in the plurality of light condensing layers may be smallerthan a wavelength of incident light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically illustrating an image sensor inaccordance with an embodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views illustrating a unit pixel ofthe image sensor shown in FIG. 1.

FIG. 3 is a diagram illustrating an image sensor including a pixel lensarray in accordance with an embodiment of the present invention.

FIG. 4 is a diagram illustrating an image sensor including a pixel lensarray in accordance with another embodiment of the present invention.

FIG. 5 is a diagram illustrating a modified example of the image sensorshown in FIG. 4.

FIG. 6 is a diagram illustrating an electronic device including an imagesensor in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention are described withreference to the accompanying drawings in order to describe the conceptof the present invention in detail to the extent that those skilled inthe art to which the present invention pertains may easily practice it.The drawings are not necessarily to scale and, in some instancesproportions of structures illustrated in the drawings may have beenexaggerated. The position and sequence of layers may be changed.Furthermore, all the layers of a multilayer structure may not be shownin the drawings (e.g., one or more additional layers may be presentbetween two illustrated layers). For example, in a multilayer structure,when a first layer is referred to as being “on” a second layer or “on” asubstrate, it not only refers to where the first layer is formeddirectly on the second layer or the substrate but also to where a thirdlayer exists between the first layer and the second layer or thesubstrate.

The embodiments of the present invention provide an image sensor withimproved performance and an electronic device having the same. As lightcondensing efficiency in unit pixels improves, performance of the imagesensor improves. In general, an image sensor may include a plurality ofunit pixels. Each of the unit pixels may include a hemispherical typemicro lens (ML) disposed over a photoelectric conversion element.Through the micro lens, incident light may be condensed and transmittedinto the photoelectric conversion element. The light condensingefficiency of the unit pixel may depend on the quality of the microlens. The light condensing efficiency may be controlled according to afocal length between the micro lens and the photoelectric conversionelement.

In a conventional micro lens, the focal length between the micro lensand the photoelectric conversion element is likely to change during aprocess of changing the curvature of the micro lens. Thus, it is noteasy to control the focal length.

The micro lens may be formed through a process of reflowing a lensforming material, for example, a resist. In such a process, it isdifficult to form a hemispherical shape with a desired curvature.Furthermore, since the micro lens is formed over a color filter layer,applicable materials are limited. In addition, the reflow process may beexpensive, may only form hemispherical shapes, and there may bedifficulties in forming micro lenses that are symmetrical and uniform.This may increases crosstalk.

The following embodiments of the present invention provide an imagesensor with improved light condensing efficiency in unit pixels and anelectronic device having the same. For this structure, each of the unitpixels may include a pixel lens having a plurality of light condensinglayers which are formed over a photoelectric conversion element. A lowerlayer of the plurality of light condensing layers has a larger area orcritical dimension (CD) than an upper layer of the plurality of lightcondensing layers. Thus, the pixel lens may have a multilayer steppedstructure. The pixel lens having the multilayer stepped structureexhibits sub-wavelength optics or sub-wavelength effects to condenseincident light. The pixel lens may effectively condense light within alimited area. Thus, the pixel lens according to an embodiment isadvantageous in increasing integration of the image sensor and mayeasily vary focal length. According to the sub-wavelength optics, anoptical effect may be obtained in a spatial scale smaller than a half ofa wavelength of incident light.

FIG. 1 is a block diagram schematically illustrating an image sensor inaccordance with an embodiment of the present invention.

As illustrated in FIG. 1, the image sensor in accordance with theembodiment of the present invention may include a pixel array 100, acorrelated double sampler (CDS) 120, an analog-to-digital converter(ADC) 130, a buffer 140, a row driver 150, a timing generator 160, acontrol register 170, and a ramp signal generator 180. The pixel array100 may include a plurality of unit pixels 110 arranged in a matrixshape.

The timing generator 160 may generate one or more control signals forcontrolling the row driver 150, the CDS 120, the ADC 130, and the rampsignal generator 180. The control register 170 may generate one or morecontrol signals for controlling the ramp signal generator 180, thetiming generator 160, and the buffer 140.

The row driver 150 may drive the pixel array 100 on a row line basis.For example, the row driver 150 may generate a select signal forselecting any one row line of a plurality of row lines. Each of the unitpixels 110 may sense incident light and output an image reset signal andan image signal to the CDS 120 through a column line. The CDS 120 mayperform sampling on the image reset signal and the image signal.

The ADC 130 may compare a ramp signal outputted from the ramp signalgenerator 180 with a sampling signal outputted from the CDS 120, andoutput a comparison signal. In response to a clock signal provided fromthe timing generator 160, the ADC 130 may count the level transitiontime of the comparison signal, and output the count value to the buffer140. The ramp signal generator 180 may generate the ramp signal undercontrol of the timing generator 150 and the control register 170.

The buffer 140 may store a plurality of digital signals outputted fromthe ADC 130, and then sense and amplify the digital signals. Thus, thebuffer 140 may include a memory (not illustrated) and a sense amplifier(not illustrated). The memory may serve to store count values. The countvalues are related to signals outputted from the plurality of unitpixels 110. The sense amplifier may serve to sense and amplify the countvalues outputted from the memory.

In the above-described image sensor, each of the unit pixels may includea pixel lens capable of improving light condensing efficiency.Hereinafter, a unit pixel including a pixel lens will be described indetail with reference to the accompanying drawings.

FIGS. 2A and 2B are cross-sectional views illustrating the unit pixel110 of the image sensor shown in FIG. 1.

As illustrated in FIGS. 2A and 2B, each of the unit pixels 110 mayinclude a substrate 210, a focusing layer 230, a pixel lens 240, a colorfilter layer 250, and an anti-reflection structure 260 or 270. Thesubstrate 210 may include a photoelectric conversion element 220. Thefocusing layer 230 may be formed over the substrate 210. The pixel lens240 may be formed over the focusing layer 230 and include a plurality oflight condensing layers in which a lower layer has a larger area orcritical dimension (CD) than an upper layer. The color filter layer 250may be formed over the focusing layer 230 to cover the pixel lens 240.The anti-reflection structure 260 or 270 may be formed over the colorfilter layer 250.

In the present embodiment, the pixel lens 240 may include a first lightcondensing layer 241 formed over the focusing layer 230 and a secondlight condensing layer 242 formed over the first light condensing layer241 and having a smaller area than the first light condensing layer 241.The first light condensing layer 241 may correspond to the lower layer,and the second light condensing layer 242 may correspond to the upperlayer. Hereinafter, the first light condensing layer is referred to as a“lower light condensing layer 241” and the second light condensing layeris referred to as an “upper light condensing layer 242”.

The substrate 210 may include a semiconductor substrate. Thesemiconductor substrate may have a single crystal state and include asilicon-containing material. That is, the substrate 210 may include asingle-crystal silicon containing material.

The photoelectric conversion element 220 may include photo diodes. Forexample, the photoelectric conversion element 220 formed over thesubstrate 210 may include a plurality of photoelectric conversion layers(not illustrated) which are vertically stacked over the substrate 210.Each of the photoelectric conversion layers may serve as a photodiodeincluding an N-type impurity region and a F-type impurity region.

The focusing layer 230 may serve to adjust a distance at which incidentlight condensed through the pixel lens 240 reaches the photoelectricconversion element 220, that is, a focal length. Due to the focusinglayer 230, the focal length may be adjusted without a variation ofcurvature, unlike a conventional device in which the focal length isadjusted using a hemispherical micro lens with a given curvature.Furthermore, a shorter focal length may be set within a limited space.The focal length may be inversely proportional to a thickness T of thefocusing layer 230. For example, the focal length may be shortened asthe thickness T of the focusing layer 230 increases, and lengthened asthe thickness T of the focusing layer 230 decreases.

To effectively transmit the incident light condensed through the pixellens 240 to the photoelectric conversion element 220, the focusing layer230 may have an area equal to or larger than that of the pixel lens 240.The focusing layer 230 may have a shape corresponding to each of theunit pixels 110. Thus, between the adjacent unit pixels 110, thefocusing layers 230 may be in contact with each other. For example, thefocusing layer 230 may have a rectangular shape.

To more effectively transmit the incident light condensed through thepixel lens 240 to the photoelectric conversion element 220, the focusinglayer 230 may have a larger refractive index than the pixel lens 240.The focusing layer 230 may include any materials having a largerrefractive index than the pixel lens 240.

Since the focusing layer 230 is positioned at the bottom of the colorfilter layer 250, the focusing layer 230 may include various materialsused in a typical semiconductor fabrication process. For example, thefocusing layer 230 may include transparent materials which includeinorganic materials such as silicon oxide, silicon nitride, and titaniumnitride. The focusing layer 230 may have a single-layer structure ormultilayer structure in which transparent materials having differentrefractive indexes are stacked. When the focusing layer 230 has themultilayer structure, the refractive index of the focusing layer 230 mayvary depending on position. A lower layer of the multilayer structuremay have a refractive index larger than an upper layer of the multilayerstructure.

The pixel lens 240 may serve as a light condensing member to condenseincident light. To improve light condensing efficiency, the pixel lens240 may have a multilayer structure in which two or more lightcondensing layers 241 and 242 are stacked. The upper light condensinglayer 242 may have a smaller area or CD than the lower light condensinglayer 241. Thus, the pixel lens 240 may have a multilayer steppedstructure. When the pixel lens 240 has the multilayer stepped structure,the difference width, that is, the widths W1 and W2 may be smaller thanthe wavelength of incident light. That is, in the pixel lens, the lowerlayer exposed by the upper layer has a smaller width than the wavelengthof incident light. More specifically, the difference in width, that is,the widths W1 and W2 between the upper light condensing layer 242 andthe lower light condensing layer 241 may be smaller than the wavelengthof the incident light of which colors are separated through the colorfilter layer 250. Through this structure, the pixel lens 240 having amultilayer stepped structure can condense light as a conventionalhemispherical lens does. This is based on the sub-wavelength optics. Thewidths W1 and W2 form step widths between the upper layer 242 and thelower layer 241 at both ends respectively, and may be equal to eachother (W1=W2) or different from each other (W1≠W2).

The plurality of light condensing layers 241 and 242 may have the sameshape, and be arranged in parallel. Specifically, the plurality of lightcondensing layers 241 and 242 may have a circular shape, a polygonalshape including a quadrangular shape, or the like.

To further improve light condensing efficiency, a thickness t2 of theupper light condensing layer 242 may be less than or equal to thethickness t1 of the lower light condensing layer 241, i.e., t1≧t2.Furthermore, to further improve light condensing efficiency, the upperlight condensing layer 242 may have a refractive index less than orequal to that of the lower light condensing layer 241. The plurality oflight condensing layers 241 and 242 may include a transparent material.When the upper light condensing layer 242 and the lower light condensinglayer 241 have the same refractive index, the upper light condensinglayer 242 and the lower light condensing layer 241 may be formed of thesame material.

Since the plurality of light condensing layers 241 and 242, that is, thepixel lens 240 is positioned at the bottom of the color filter layer250, the plurality of light condensing layers 241 and 242 may includevarious materials used in a typical semiconductor fabrication process.For example, the plurality of light condensing layers 241 and 242 mayinclude transparent materials which may include inorganic materials suchas silicon oxide, silicon nitride, and titanium nitride. The lightcondensing layers 241 and 242 may have a single-layer structure ormultilayer structure in which transparent materials having differentrefractive indexes are stacked. When each of the plurality of lightcondensing layers 241 and 242 has the multilayer structure, therefractive index of each light condensing layer may vary depending onposition. An upper layer of each light condensing layer may have arefractive index that is less than a lower layer of each lightcondensing layer. That is, the refractive index of each light condensinglayer may increase as the light condensing layers are adjacent to thephotoelectric conversion element 220 or the focusing layer 230.

The color filter layer 250 for color separation may be formed over thefocusing layer 230 to cover the pixel lens 240, and have a flat surface.Since the color filter layer 250 is in contact with the pixel lens 240and covers the pixel lens 240, light transmission between the colorfilter layer 250 and the pixel lens 240 may be improved. That is, lightcondensing efficiency may be improved. The color filter layer 250 mayinclude a red filter, a green filter, a blue filter, a cyan filter, ayellow filter, a magenta filter, an infrared pass filter, an infraredcutoff filter, a white filter, or a combination thereof. To furtherimprove the light condensing efficiency, the color filter layer 250 mayhave a smaller refractive index than the pixel lens 240.

The anti-reflection structure 260 or 270 may be formed over the colorfilter layer 250 and include an anti-reflection layer 260 shown in FIG.2A or a hemispherical lens 270 shown in FIG. 2B. The anti-reflectionlayer 260 may include two or more material layers which have differentrefractive indexes and are alternately stacked one or more times. Thehemispherical lens 270 may not only prevent reflection of incidentlight, but also condense light incident on the pixel lens 240.

As the image sensor having the above-described structure includes thepixel lens 240 having a multilayer stepped structure, the lightcondensing efficiency in the unit pixel 110 may be improved.Furthermore, as the color filter layer 250 has a shape to cover thepixel lens 240, the light condensing efficiency in the unit pixel 110may be further improved. As the light condensing efficiency in the unitpixel 110 is improved, quantum efficiency in the photoelectricconversion element 220 may also be improved. As a result, theperformance of the image sensor may be improved.

As seen in FIG. 1, the image sensor includes the pixel array 100 inwhich the plurality of unit pixels 110 has been arrayed in atwo-dimensional manner. As a high-integration image sensor is beingdeveloped, the characteristics of the image sensor are deteriorated dueto a difference in the chief ray angle (CRA) and the amount of incidentlight according to the positions of unit pixels 110 in the pixel array100. Specifically, shading variations are generated because the amountof incident light at the edge of the pixel array 100 is smaller than theamount of incident light at the center of the pixel array 100, therebydirectly deteriorating picture quality.

Accordingly, in the following embodiments, an image sensor including apixel lens array, which is capable of compensating for a difference inthe amount of incident light attributable to the positions of unitpixels in the pixel array, is described in detail with reference to theaccompanying drawings. The same reference numerals to be used for thesame configuration.

In FIGS. 3 to 5, a pixel array 100 in which a plurality of unit pixelshas been arrayed in a two-dimensional manner may include a first pixel110A to a fifth pixel 110E. The first pixel 110A to the fifth pixel 110Ehave been illustrated in order to describe a change in the shapes ofpixel lenses 240 attributable to the positions of the first to fifthpixels 110A to 110E within the pixel array 100. Specifically, the pixelarray 100 may include the first pixel 110A placed at the center of thepixel array 100, the second pixel 110B placed at the edge of a row lineincluding the first pixel 110A, the third pixel 110C placed in themiddle of the first pixel 110A and the second pixel 110B in the row lineincluding the first pixel 110A, the fourth pixel 110D placed at thecorner of an edge of the pixel array 100, and the fifth pixel 110Eplaced in the middle of the first pixel 110A and the fourth pixel 110Din a line that is extended from the first pixel 110A to the fourth pixel110D.

FIG. 3 is a diagram illustrating an image sensor including a pixel lensarray in accordance with an embodiment of the present invention.

As illustrated in FIG. 3, in the pixel array 100 in which the pluralityof unit pixels 110A, 110B, 1100, 110D, and 110E have been arrayed in atwo-dimensional manner, each of the plurality of unit pixels 110A 1108,110C, 110D, and 110E may include a photoelectric conversion element andthe pixel lens 240 formed on the photoelectric conversion element andconfigured to include a plurality of light condensing layers in which alower light condensing layer 241 has a larger area than an upper lightcondensing layer 242. In this case, the pixel lens 240 may have a shapechanging according to a position of each of the plurality of unit pixels110A, 110B, 110C, 110, and 110E from the center of the pixel array 100to the edge of the pixel array 100.

Specifically, the pixel lens 240 may have symmetry on the basis of thecentral axis (or optical axis) of each of the plurality of unit pixels110A, 110B, 110C, 110D, and 110E, and the area (or size) of the pixellens 240 may be gradually increased from the center of the pixel array100 to the edge of the pixel array 100.

That is, the pixel lens 240 of the first pixel 110A placed at the centerof the pixel array 100 may have the smallest area. The pixel lenses 240of the second pixel 110B and the fourth pixel 110D placed at the edgesof the pixel lens 240 may have the greatest size. The area of the pixellens 240 may be linearly increased from the center of the pixel array100 to the edge of the pixel array 100.

A width of the lower light condensing layer 241 exposed by the upperlight condensing layer 242 in the pixel lens 240 may be constantregardless of the position of the pixel lens 240 in the pixel array 100.That is, the width of the lower light condensing layer 241 exposed bythe upper light condensing layer 242 in the pixel lens 240 of each ofthe first pixel 110A to the fifth pixel 110E may be the same.Furthermore, the width of the lower light condensing layer 241 exposedby the upper light condensing layer 242 may be constant regardless ofthe direction because the pixel lens 240 is symmetrical based on thecentral axis of each of the plurality of unit pixels 110A, 110B, 110C,110D, and 110E. In this case, the width of the lower light condensinglayer 241 exposed by the upper light condensing layer 242 in the pixellens 240 may be smaller than the wavelength of incident light.

As described above, the pixel lens 240 has symmetry on the basis of thecentral axis (or optical axis) of each of the plurality of unit pixels110A, 110B, 110C, 110D and 110E, and the area of the pixel lens 240 isgradually increased from the center of the pixel array 100 to the edgeof the pixel array 100. Accordingly, the amount of incident light at theedge of the pixel array 100 may be increased. Furthermore, a differencein the amount of incident light between the center and edge of the pixelarray 100 may be reduced.

FIG. 4 is a diagram illustrating an image sensor including a pixel lensarray in accordance with another embodiment of the present invention,and FIG. 5 is a diagram illustrating a modified example of the imagesensor shown in FIG. 4.

As illustrated in FIGS. 4 and 5, in the pixel array 100 in which theplurality of unit pixels 110A, 110B, 110C, 110E) and 110E have beenarrayed in a two-dimensional manner, each of the plurality of unitpixels 110A, 110B, 1100, 110D, and 110E may include a photoelectricconversion element and the pixel lens 240 formed on the photoelectricconversion element and configured to have a plurality of lightcondensing layers in which an upper light condensing layer 242 has asmaller area than a lower light condensing layer 241. The pixel lens 240may have a shape changing according to a position of each of theplurality of unit pixels 110A, 110B, 110C, 110D, and 110E from thecenter of the pixel array 100 to the edge of the pixel array 100.

Specifically, the pixel lens 240 of each of the plurality of unit pixels110A, 110B, 110C, 110D, and 110E has the same area (or size), andasymmetry of the pixel lens 240 may be gradually increased from thecenter of the pixel array 100 to the edge of the pixel array 100 on thebasis of the central axis of each of the plurality of unit pixels 110A,110B, 110C, 110D, and 110E.

The pixel lens 240 of the first pixel 110A placed at the center of thepixel array 100 may have symmetry on the basis of the central axis ofthe first pixel 110A. The pixel lenses 240 of the second pixel 110B andthe fourth pixel 110D may have the greatest asymmetry on the basis ofthe central axis of each of the second pixel 110B and the fourth pixel110D.

When the asymmetry of the pixel lens 240 is gradually increased from thecenter of the pixel array 100 to the edge of the pixel array 100 on thebasis of the central axis of each of the plurality of unit pixels 110A,110B, 110C, 110D, and 110E as described above, it may mean that amaximum width of the lower light condensing layer 241 exposed by theupper light condensing layer 242 in the pixel lens 240 is graduallyincreased from the center of the pixel array 100 to the edge of thepixel array 100. The maximum width may be linearly increased.Furthermore, the maximum width of the lower light condensing layer 241exposed by the upper light condensing layer 242 in the pixel lens 240may be smaller than the wavelength of incident light. For reference,since the pixel lens 240 has asymmetry, a width of the lower lightcondensing layer 241 exposed by the upper light condensing layer 242 inthe pixel lens 240 may be different depending on direction.

More specifically, referring to FIG. 4, the upper light condensing layer242 of the pixel lens 240 may be shifted more to the center of the pixelarray 100 on the basis of the central axis of each of the plurality ofunit pixels 110A, 110B, 110C, 110D, and 110E as the pixel lens 240 ispositioned from the center of the pixel array 100 to the edge of thepixel array 100. The pixel lens 240 is configured to have a close shapein a chief ray angle (CRA) direction in accordance with the principle ofa grated index (GRIN) lens, thereby increasing the amount of incidentlight at the edge of the pixel array 100.

Referring to FIG. 5, in opposition to FIG. 4, the upper light condensinglayer 242 of the pixel lens 240 may be shifted more to the edge of thepixel array 100 on the basis of the central axis of each of theplurality of unit pixels 110A, 110B, 110C, 110D, and 110E as the pixellens 240 is positioned from the center of the pixel array 100 to theedge of the pixel array 100. The amount of incident light at the edge ofthe pixel array 100 may be increased in such a manner that incidentlight emitted to outside the pixel lens 240 is guided to preventcrosstalk.

As described above, the pixel lens 240 of each of the plurality of unitpixels 110A, 110B, 110C, 110D, and 110E has the same area, and theasymmetry of the pixel lens 240 is gradually increased from the centerof the pixel array 100 to the edge of the pixel array 100 on the basisof the central axis of each of the plurality of unit pixels 110A, 110B,110C, 110D, and 110E. Accordingly, the amount of incident light at theedge of the pixel array 100 may be increased. Furthermore, a differencein the amount of incident light between the center and edge of the pixelarray 100 may be reduced.

This technology may improve light collection efficiency in a unit pixelbecause the pixel lens is included.

Furthermore, the amount of incident light at the edge of the pixel arraymay be increased and a difference in the amount of incident lightbetween the center and edge of the pixel array may be reduced bycontrolling the shapes of pixel lenses depending on the positions of thepixel lenses within the pixel array.

As described above, quantum efficiency in a photoelectric conversionelement may be improved because light collection efficiency and theamount of incident light in a unit pixel are increased. As a result,performance of an image sensor may be improved.

The image sensor in accordance with an embodiment of the presentinvention may be used in various electronic devices or systems.Hereafter, the image sensor in accordance with an embodiment of thepresent invention which is applied to a camera will be described withreference to FIG. 6.

FIG. 6 is a diagram briefly illustrating an electronic device includingan image sensor in accordance with an embodiment of the presentinvention.

Referring to FIG. 6, the electronic device including the image sensor300 in accordance with the embodiment of the present invention mayinclude a camera capable of taking a still image or moving image. Theelectronic device may include the image sensor 300, an optical system oroptical lens 310, a shutter unit 311, a driving unit 313 forcontrolling/driving the image sensor 300 and the shutter unit 311 and asignal processing unit 312.

The optical system 310 may guide image light, that is, incident light,from an object to the pixel array 100 (refer to FIG. 1) of the imagesensor 300. The optical system 310 may include a plurality of opticallenses. The shutter unit 311 may control a light irradiation period anda light shield period for the image sensor 300. The driving unit 313 maycontrol a transmission operation of the image sensor 300 and a shutteroperation of the shutter unit 311. The signal processing unit 312 mayprocess signals outputted from the image sensor 300 in various manners.The processed image signals Dout may be stored in a storage medium suchas a memory or outputted to a monitor or the like.

Although various embodiments have been described for illustrativepurposes, it will be apparent to those skilled in the art that variouschanges and modifications may be made without departing from the spiritand scope of the invention as defined in the following claims.

What is claimed is:
 1. An image sensor comprising: a pixel arrayincluding a plurality of unit pixels, wherein each of the plurality ofunit pixels comprises: a photoelectric conversion element; and a pixellens over the photoelectric conversion element and comprising aplurality of light condensing layers in which a lower layer has a largerarea than an upper layer, wherein the pixel lens has a shape changingbased on its position from a center of the pixel array to an edge of thepixel array, wherein each of the plurality of unit pixels furthercomprises: a focusing layer between the photoelectric conversion elementand the pixel lens; a color filter layer covering an entire surface ofthe pixel lens; and an anti-reflection structure over the color filterlayer, wherein each of the plurality of light condensing layers has aflat surface.
 2. The image sensor of claim 1, wherein the pixel lens hasa multilayer stepped shape.
 3. The image sensor of claim 1, wherein theplurality of light condensing layers of the pixel lens have the sameshape and are parallel to each other.
 4. The image sensor of claim 1,wherein a thickness of the upper layer of the plurality of lightcondensing layers is less than or equal to a thickness of the lowerlayer.
 5. The image sensor of claim 1, wherein a refractive index of theupper layer of the plurality of light condensing layers is less than orequal to a refractive index of the lower layer.
 6. The image sensor ofclaim 1, wherein: the pixel lens is symmetrical based on a central axisof each of the plurality of unit pixels, and an area of the pixel lensis gradually increased from the center of the pixel array to the edge ofthe pixel array.
 7. The image sensor of claim 6, wherein a width of thelower layer exposed by the upper layer in the plurality of lightcondensing layers is constant regardless of its position in the pixelarray.
 8. The image sensor of claim 7, wherein the width of the lowerlayer exposed by the upper layer is smaller than a wavelength ofincident light.
 9. The image sensor of claim 1, wherein: the pixellenses of each of the plurality of unit pixels are the same size, andasymmetry of the pixel lens is gradually increased based on a centralaxis of each of the plurality of unit pixels going from the center ofthe pixel array to the edge of the pixel array.
 10. The image sensor ofclaim 9, wherein the upper layer of the plurality of light condensinglayers is shifted more to the center of the pixel array based on thecentral axis of each of the plurality of unit pixels going from thecenter of the pixel array to the edge of the pixel array.
 11. The imagesensor of claim 9, wherein the upper layer of the plurality of lightcondensing layers is shifted more to the edge of the pixel array basedon the central axis of each of the plurality of unit pixels going fromthe center of the pixel array to the edge of the pixel array.
 12. Theimage sensor of claim 9, wherein a maximum width of the lower layerexposed by the upper layer in the plurality of light condensing layersis gradually increased going from the center of the pixel array to theedge of the pixel array.
 13. The image sensor of claim 12, wherein themaximum width of the lower layer exposed by the upper layer is smallerthan a wavelength of incident light.
 14. An electronic devicecomprising: an optical system; an image sensor suitable for receivinglight from the optical system and comprising a pixel array including aplurality of unit pixels; and a signal processing unit suitable forperforming a signal processing operation on a signal output from theimage sensor, wherein each of the plurality of unit pixels of the imagesensor comprises: a photoelectric conversion element; and a pixel lensover the photoelectric conversion element and comprising a plurality oflight condensing layers in which a lower layer has a larger area than anupper layer, wherein the pixel lens has a shape changing based on aposition of a corresponding unit pixel going from a center of the pixelarray to an edge of the pixel array, wherein each of the plurality ofunit pixels further comprises: a focusing layer between thephotoelectric conversion element and the pixel lens; a color filterlayer covering an entire surface of the pixel lens; and ananti-reflection structure over the color filter layer, wherein each ofthe plurality of light condensing layers has a flat surface.
 15. Theelectronic device of claim 14, wherein: the pixel lens is symmetricalbased on a central axis of each of the plurality of unit pixels, and anarea of the pixel lens is gradually increased going from the center ofthe pixel array to the edge of the pixel array.
 16. The electronicdevice of claim 14, wherein: the pixel lenses of the unit pixels are thesame size, and asymmetry of the pixel lens is gradually increased basedon a central axis of each of the plurality of unit pixels from thecenter of the pixel array to the edge of the pixel array.
 17. Theelectronic device of claim 14, wherein the pixel lens has a multilayerstepped shape.
 18. The electronic device of claim 14, wherein a width ofthe lower layer exposed by the upper layer in the plurality of lightcondensing layers is smaller than a wavelength of incident light.